1. Field of the Invention
The invention relates to a grate bar. The grate bar may be used in a waste-incinerator grate or a cement clinker cooler, or a similar system.
2. Description of Relevant Art
Waste incineration (briefly, ‘incineration’) is commonly referred to as thermal treatment of waste to combust organic substances of waste material. To this end the waste is deposited on top of a waste-incinerator grate, heated and brought in contact with air or another oxygen source. Typically, the waste is conveyed to an outlet as a results of reciprocal movement of at least some of the grate bars or other means, while being combusted. The grate bars may be cooled by air that is injected via the grate bars into the waste material. Alternatively, water cooling is an option, but such approach has the drawback of higher installation cost and the fact that energy is removed at a low temperature, thereby reducing the efficiency of heat recovery systems such as, e.g., a turbine operating to convert heat released in the incinerator to electric energy.
Typically, the incinerator grate is a stepped grate with rows of grate bars forming steps. Each row in such grate and thus each grate bar has a rear end (facing the waste inlet) and a front end (facing in the conveying direction that is a direction in which the material is being conveyed during the operation of the system employing the grate). The rear end of each row is typically supported by cross beams, while the front end resides on the rear end of the next neighboring row of grate bars in the conveying direction. As a result of reciprocal movement of the rows, the waste is conveyed forward towards an outlet of the system, for withdrawal of residues from the incinerator.
EP 1 008 806 suggests a metallic grate bar for a waste incinerator. On top of the grate bar there is a wear layer of a ceramic composite material. The wear layer is formed by a metallic frame structure enclosing ceramic inserts. The metallic frame resembles a honeycomb structure, into which preformed ceramic inserts are positioned. Alternatively, the metallic frame may provide oval spaces for insertion of complementary ceramic inserts.
In BE 383112 A, a firing grate of iron lattice bars is disclosed. The lattice bars have recesses enabling crossing bars to fit together. But the recesses have a bent shape and thus fitting a first bar into a recess of a second bar requires heating and bending such first bar during the process of insertion, which is difficult and expensive.
DE 197 14 573 C1 teaches a waste-incinerator grate that is completely made of ceramic material. The grate is assembled from dried but not yet fired preformed grate elements. After assembly, the grate is fired to form a monolithic ceramic structure.
DE 10 2009 016 523 A1 discloses a grate bar for an incinerator with a base structure formed by steel casting. On top of the base structure there exists a temperature resistant ceramic top plate. Between the cast steel base and the ceramic top plate there is a ceramic fiber material, disposed for thermal isolation of the cast steel base from the top plate.
The authors of DE 20 2012 001 080 U1 suggest a waste incinerator grate bar with a support element that is enclosed in a fiber enforced glass body replacing ceramic materials. The temperature range for using the so-obtained waste incinerator grate bars depends on the softening temperature of the glass and is between 300° C. and 1770° C., depending on the choice of glass.
US 2004/159269 A1 relates to a gasifier combustor for drying and subsequent gasification of solid fuel. The resultant gas is subsequently moved through a duct to a combustion chamber. The gasifier combustor comprises a grate segment for a burner with an array of cavities being arranged in a honeycomb structure. The cavities are filled with a refractory material, e.g. a ceramic material.
Despite of these suggestions, grate bars for waste incineration are in practice mostly still made of heat resistant metal cast, e.g. of European Standard Steel Grade (EN 10027-2) 1.4823, by sand molds or using the lost foam casting method. The raw demolded grate bars are subsequently machined to provide the required precision of the dimensions. These grate bars are expensive and have a limited life span.